A fuel meter is the most accurate way to determine a boat’s fuel consumption. To estimate a boat’s fuel consumption, multiply the engine’s specific fuel consumption by the horsepower of the engine, and divide the result by the weight in pounds per gallon of fuel.
Due to the difficulty in measuring distance and the different conditions encountered on the water, boat fuel consumption is measured in gallons per hour. When estimating fuel consumption, the calculation varies depending on whether the fuel is gasoline or diesel. The specific fuel consumption of an engine is how much fuel it burns in pounds per unit of horsepower. For a four-stroke gasoline engine, this is around 0.5 pounds of fuel, while a diesel engine uses around 0.4 pounds of fuel. To convert to gallons, the weight per gallon of fuel is needed, which for gasoline is approximately 6.1 pounds per gallon, while diesel weighs approximately 7.2 pounds per gallon.
To estimate the fuel consumption in gallons per hour of a 200-horsepower gasoline engine, multiply the specific fuel consumption of 0.5 times 200 and divide by 6.1, yielding a result of 16.4 gallons per hour.
For a 200-horsepower diesel engine, a specific fuel consumption of 0.4 multiplied by the horsepower of 200 and divided by the diesel fuel weight of 7.2 pounds per gallon equals a fuel consumption of 11.1 gallons per hour.